The best way to start with arranging throw pillows is to find the "ONE" pillow that just speaks to you. Browse online at sites like etsy, zgallery, even target has some wonderful lines at super prices.
Mix patterns: If you want all the same color tones, mix it up by putting a print with stripes, dots, or a textured solid.
Layer the pillows on the couch in groupings with different sizes to add demintion. I like to keep them in groups of three.
If you like pillows all the way across a surface keep it in odd numbers and different sizes.
Pillows should almost always be down filled, it keeps them looking full and happy on your sofa. If you want them to have a comfy, cozy look, give them a soft karate chop in the middle.
Pillow pictures from etsy, plum cushion, 6th street design school and Thomas o'brien.